In a traditional power semiconductor device, a large current is generally flowed or a high voltage is applied through the leads of the device. In addition, with the development of main stream technology, the device size often needs to be minimized, which causes the insulating materials surrounding the leads being extremely closer to each other and subjected to electric polarization, so that the insulating materials are electrified to affect the normal operation of the device, or to cause the potential safety hazards; particularly, a creep-age phenomenon is increased under humidity or dust environments. In standard for safety of electric appliances in North America, ANSI/UL standard is commonly used for evaluation. An electric safety distance is a standard requirement for safety of electric appliances. For restraining the creep-age phenomenon, it is important to control the electric clearance or the creep-age distance and other related parameters.
A conventional TO-220 device is as shown in FIG. 1A. The die paddle of the power device for attaching the power MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) chips are all completely sealed in a plastic package body 10. Leads 11-13 and a heat sink 14 are all exposed out of the plastic package body 10. The outer leads 11 and 13 are separated from the die paddle as a gate lead and a source lead respectively, the inner lead 12 is generally connected with the die paddle as a drain lead. The leads 11-13 are arranged in side by side with equidistance. In this device, the leads 11-13 are much closer to each other so that their creep-age distance does not comply with the requirements under a high voltage condition, for example, a distance between a symmetric center line of the lead 12 along its length direction and that of the leads 11 or 13 along its length direction is about 2.54 mm, while the narrowest distance between the part of the lead 12 closest to the plastic package body and the part of the lead 11 (or 13) closest to the plastic package body is only about 1.27 mm, thus, such lead distance is very likely to cause the creep-age phenomenon. To overcome this problem, U.S. Pat. No. 6,255,722B1 discloses a device structure as shown in FIG. 1B. In FIG. 1B, fine slots 70 and 71 are formed on the side face of a plastic package body 60 between an inner lead 24 and two outer leads 23 and 25 at its both sides. The fine slot 70 increases the creep-age distance between the leads 23 and 24, and the fine slot 71 increases the creep-age distance between the leads 24 and 25. In addition, in U.S. Pat. No. 6,291,262B1, a slot body is formed in a side wall of a plastic package body 50 located between two outer leads 38 (as shown in top view of FIG. 1C-1), furthermore, the inner lead 44 and the outer leads 38 are respectively arranged on different horizontal planes (as shown in side view of FIG. 1C-2), thus a creep-age distance can also be adjusted.
However, in the conventional devices described above, the method of changing the creep-age distance is very limited; especially it cannot restrain the creep-age phenomenon under the harsh environment when a high voltage is applied on the drain lead or source lead. Based on these problems, various embodiments provided in the invention are proposed.